Valve Selection Checklist: 10 Parameters Procurement Engineers Must Specify

Every experienced valve procurement engineer has a story about the order that went wrong — the WCB ball valves delivered to an HCl service line, the Class 150 gate valves installed in a Class 300 system, or the globe valves without fire-safe design fitted in a hydrocarbon ESD circuit. In almost every case, the root cause is an incomplete specification. Valve manufacturers supply exactly what is specified — and if the specification omits a critical parameter, they supply the standard default. This checklist provides the 10 parameters that must be defined in every valve RFQ or purchase order to eliminate ambiguity, prevent wrong-material supply, and ensure valves are code-compliant on day one.

Parameter 1: Valve Type — Isolation, Control, or Check

The first decision is the valve function: isolation valves (full open / full closed service) include ball, gate, and butterfly valves; control valves (modulating flow) include globe, needle, butterfly (throttling), and dedicated control valve types; check valves (non-return) include swing check, dual-plate wafer check, axial flow check, and lift check types. Mixing up isolation and control types is surprisingly common in early-stage procurement — specifying a gate valve for a throttling application leads to gate vibration, erosion, and premature failure. Define the service: on-off isolation, throttling, or non-return.

Parameter 2: Size — DN (Nominal Diameter) or NPS (Nominal Pipe Size)

Valve size must be specified in both NPS (inch) or DN (mm) consistent with the applicable piping code and line list. Common errors: specifying valve size without confirming it matches the connected pipe schedule (a DN50 valve flanged face matches regardless of pipe wall thickness, but a SW or BW valve requires bore matching to pipe schedule); specifying a reduced-bore ball valve where full-bore is required for pigging or minimum pressure-drop service; and forgetting to specify face-to-face dimension standard (ASME B16.10 Short Pattern vs Long Pattern for gate valves, or ISA face-to-face for control valves).

Parameter 3: Pressure Class — ANSI/ASME Class 150 to 2500

ASME B16.34 defines seven pressure classes: 150, 300, 600, 900, 1500, and 2500. The pressure class determines the maximum allowable working pressure (MAWP) at a given temperature for each material group. Common errors: specifying Class 150 for a system with a maximum operating pressure of 19 barg at 200°C — Class 150 WCB is rated for 19.6 barg at 200°C but this leaves essentially zero margin; Class 300 should be specified if the system design pressure approaches the Class 150 limit. Always cross-reference the design pressure + design temperature with ASME B16.34 Table 2 for the specific material group to confirm the class is adequate.

Parameter 4: Body Material

Body material must be specified as the ASTM designation (not a colloquial name). Specifying 'stainless steel' is insufficient — CF8M (316 SS cast), CF8 (304 SS cast), CF3M (316L SS cast), and F316L (316L forged) are all 'stainless steel' but have different mechanical properties, carbon content, and welding implications. For body material: specify ASTM grade (e.g., A216 WCB, A351 CF8M, A182 F316, A182 F51), include NACE MR0175 requirement if H2S service, specify impact test temperature if below −29°C service, and specify any special chemistry requirements (low carbon grade CF3M vs CF8M for improved weldability).

Parameter 5: End Connection

End connection type determines how the valve connects to piping. The four main types are: flanged (raised face RF, flat face FF, ring-type joint RTJ) per ASME B16.5 (DN15–DN600) or B16.47 (DN650–DN1500); butt weld (BW) per ASME B16.25, scheduled to match pipe; socket weld (SW) per ASME B16.11, for small bore DN15–DN50; and threaded (NPT/BSPT) per ASME B1.20.1 for instrument and utility valves. For flanged valves: always specify flange facing — RF is standard for Class 150–600; RTJ is standard for Class 900+. Specifying 'flanged' without facing type risks receiving FF (flat face) flanges that cannot be bolted to RF-faced piping without gasket modification.

Parameter 6: Trim Material

Trim refers to the internal components that contact the process fluid: stem, disc (ball/gate/plug/disc), seats, and packing. For a ball valve, trim includes ball material, stem material, and seat ring material. Common trim specifications: 'SS 316 trim' for standard chemical service; 'Stellite 6 hard-faced trim' for erosive or high-temperature service where seat wear is a concern; 'Hastelloy C-276 trim' for aggressive acid service with CF8M body; 'PTFE seats' for soft-seated ball valves in clean service; 'metal seats (Stellite overlay)' for fire-safe ball valves and high-temperature service. Always specify stem material separately if the process fluid is corrosive — a SS 316 stem in H2S service requires NACE qualification even if the body is WCB.

Parameter 7: Service and Design Conditions

The full service data sheet must include: process fluid identity and phase (liquid, gas, two-phase), concentration if relevant (e.g., H2SO4 at 98%), design temperature (minimum and maximum), design pressure (maximum allowable working pressure), normal operating pressure and temperature, flow rate and Cv/Kv requirement if control or check valve, specific gravity or density at operating conditions, and viscosity if relevant (for control valve Cv sizing). H2S content (mole % or ppm) must be stated for any oil and gas service to trigger NACE MR0175 compliance. Chloride content must be stated for any aqueous service to determine if SS 316 or duplex is required.

Parameter 8: Standards Compliance

The applicable standards must be explicitly stated in the purchase order. Standard clauses for common valve types: ball valves — API 6D (pipeline service), API 608 (general purpose), BS 5351, ASME B16.34; gate and globe valves — API 600 (bolted bonnet), API 602 (compact, SW/BW small bore), BS 1414 (gate), BS 1873 (globe); butterfly valves — API 609, AWWA C504 (water utility), EN 593; check valves — API 594 (wafer and lug), API 6D (pipeline), EN 13709. NACE MR0175 / ISO 15156 for sour service. PED 2014/68/EU Category III for European projects (requires Notified Body certification). ISO 15848 Class A for fugitive emissions service.

Parameter 9: Testing Requirements

Valve test requirements must be specified at order stage — requesting API 598 test reports after the valves have been manufactured and shipped is too late. Standard test specifications: API 598 shell test (hydrostatic, 1.5× pressure rating, 3-minute hold), seat test (hydrostatic or pneumatic, 1.1× pressure rating), and backseat test (rising stem valves); ISO 5208 (European equivalent of API 598, with Rate A, B, C, D leakage allowances for seats); ASME B16.34 hydrostatic shell test; fire test per API 607 (soft-seated valves) or API 6FA (all valve types) for fire-safe specification; PMI (Positive Material Identification) by XRF on all stainless and alloy steel pressure parts; Charpy impact test for low-temperature service; HIC/SSC test per NACE TM0284/TM0177 for sour service; NDE (non-destructive examination) per ASME VIII Div. 1 or API 598 for critical service.

Parameter 10: Actuation and Accessories

Specify whether the valve is to be supplied manual (handwheel, lever, or gear operator) or actuated. For actuated valves, state: actuator type (pneumatic scotch-yoke, rack-and-pinion, electric multi-turn, hydraulic); fail-safe action (fail open, fail closed, fail in last position); supply pressure for pneumatic actuators (typically 4–7 bar instrument air); electrical supply for electric actuators (220V/415V/480V, 50Hz/60Hz); control signal type (4-20mA, 0-10V, HART, PROFIBUS, Foundation Fieldbus); accessories required (solenoid valve, limit switches, position feedback transmitter, manual override, handwheel declutch, explosion-proof (EExd) enclosure for hazardous area); and SIL rating (IEC 61511 SIL 2 or SIL 3 for ESD service).

Common Specification Mistakes and How to Avoid Them

• Specifying 'ANSI Class 150 carbon steel ball valve' without body material ASTM grade — manufacturer defaults to lowest-cost grade
• Omitting end connection facing type — RF vs FF makes a joint leak if mismatched
• Not specifying NACE MR0175 for H2S-containing streams — non-NACE trim will fail by SSC in sour gas service
• Ordering API 598 test certificates as an afterthought — some manufacturers do not routinely keep records; request at order stage
• Specifying manual valve when an actuator is needed for remote isolation — retrofitting actuators on installed valves is expensive
• Specifying soft-seated ball valves for fire-zone service without API 607 fire-safe requirement
• Using inch sizing (e.g., '2 inch') without specifying NPS or DN — creates ambiguity with DN50 vs DN65 in some European catalogs

RFQ Turnaround Tips

To get fast and accurate quotations from valve suppliers: always attach a valve datasheet (VDS) or line list table rather than describing requirements in prose; specify all 10 parameters above in the datasheet; include quantity, delivery date required, and delivery destination in the first communication; state the applicable project standard or company specification (e.g., BP GS 142-1, Shell DEP, Aramco SAES) if applicable; and confirm whether TR (Third Party Inspection) is required and by which TPIA (SGS, Bureau Veritas, TÜV, Lloyds, DNV). A complete RFQ with all 10 parameters specified can receive a firm quotation in 24–48 hours. An incomplete RFQ requires multiple rounds of technical clarification and can take 5–10 days to resolve.